FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-rc-b68)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b68, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

EXTRA RELEVANT SYSTEM CONFIGURATION :
using visual style/theme from http://osx.portraitofakite.com

A DESCRIPTION OF THE PROBLEM :
  Bug ID 5106661 claims to have been fixed in the first release candidate, Jan 2006 of Mustang. True, many components (scroll bars, small JButtons, etc.) are rendered correctly, however JComboBoxes are obviously not:

- The JComboBox height is too tall.
- The JComboBox appears to have too wide of a padding inside (i.e., the button and text are indented too far from the left and right edges of the JComboBox.
- The up and down arrows on the JComboBoxes button have white borders.
- The JComboBox is drawn with the wrong border (on my particular config, it has no border at all)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Install the Mac OS X theme for Windows XP from http://osx.portraitofakite.com
Make a small test application that opens the Swing JFileChooser dialog.
Examine how this dialog compares to a native Open dialog, also affected by the theme, such as in Mozilla's Firefox browser

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
If native apps can render JComboBoxes correctly with an XP theme, then so should Mustang.
ACTUAL -
JComboBoxes are too tall, unbordered, and have exta padding, and poor spinner buttons on the pull-down button, compared to native ComboBoxes

REPRODUCIBILITY :
This bug can be reproduced always.